1. Field of Invention
The invention relates to a light driving apparatus and a driving-control method of lights, and, in particular, to a digital controlled multi-light driving apparatus for a large size flat panel display and a driving-control method of lights having a sequential flashing function.
2. Related Art
Flat panel displays have become increasingly popular in recent years, with liquid crystal displays (LCDs) garnering the most widespread acceptance. Conventional LCDs are typically employed as personal computer monitors and have a screen size of 15″ or less. As manufacturing technology has developed, a variety of display sizes have come to be employed for different purposes, including use as TV displays. When employed for this purpose, a flat panel LCD with a screen size of 30″ or larger is desirable. Accordingly, an LCD of this size requires a greater number of lights to provide adequate brightness. For example, an LCD with a screen size of 40″ may require up to 30 lights.
When the number of lights is increased, however, an accompanying problem of poor brightness uniformity between lights arises. In addition, the number of light driving apparatuses for driving the lights is also increased. For example, regarding the conventional light driving apparatus, usually only two cold cathode fluorescent lamps (CCFLs) can be driven at the same time by one transformer. Thus, for an LCD with a large screen size requiring increased number of lights, the number of required light driving apparatuses is also increased, and manufacturing costs thereof increase as a result.
As previously mentioned, the conventional LCD typically employs CCFLs as backlights thereof. To induce the CCFL or CCFLs to light, a light driving apparatus with an inverter is typically used. Referring to FIG. 1, a conventional light driving apparatus 1 mainly includes a current adjusting circuit 11, an oscillation step-up circuit 12, a detecting circuit 13, and a feedback control circuit 14.
The current adjusting circuit 11 is controlled by the feedback control circuit 14 and properly adjusts an external DC source, which is then input to the oscillation step-up circuit 12. The oscillation step-up circuit 12 converts the input DC source into an AC signal and amplifies the AC signal. The amplified AC signal is then provided to the CCFL 2, which serves as the light, so that the CCFL 2 can then light. Furthermore, the detecting circuit 13 detects a feedback signal, such as a current signal or a voltage signal, from one end of the CCFL 2. The feedback signal is then transmitted to the feedback control circuit 14. The feedback control circuit 14 controls the current adjusting circuit 11 according to the feedback signal, so that the current adjusting circuit 11 can output a suitable current level. It should be noted that the conventional feedback control circuit 14 is an analog feedback control circuit.
When the number of lights is increased, the number of required light driving apparatuses 1 is increased accordingly. In an LCD with a large screen size, a plurality of circuits, each of which includes the current adjusting circuit 11, oscillation step-up circuit 12, detecting circuit 13 and feedback control circuit 14, are necessary at the same time. Since the lights are driven by different driving apparatuses 1, which are independent from one another, the brightness uniformity adjustment or phase matching between lights cannot be efficiently achieved, resulting in poor display quality.
Therefore, it is an important subjective to prevent the above-mentioned problems, so as to improve the quality of an LCD with a large screen size and reduce manufacturing costs.
Nowadays, liquid crystal displays (LCD) are being used widely. They can be found on computer monitors, touch-screens for man-machine interface and home televisions. As popularity grows, its technical performance becomes more demanding in parameters such as viewing angle, contrast ratio, color saturation, and response time.
Among all the performance parameters, quick response time has always been one of the most sought-after items in improving motion picture quality. Low quality LCD with slow response time often causes picture blurring while viewing moving objects. This may not be a major issue if the LCD is just for a desktop computer monitor on which most of the pictures are still all the time. However, if the LCD is for home televisions, quicker response time is a must.
Besides the response time, there is a fundamental technical issue, the display type (or mode), that limits the LCD motion picture quality. The CRT display device, the predecessor of LCD, displays pictures by tracing out the images on a glass screen with a single scanning electron beam. Therefore, at any given moment, only a small fraction of the glass screen will be lightened while being scanned across by the electron beam. CRT display device cannot hold still the complete picture to be displayed on the glass screen. Actually, it displays pictures dot-by-dot and line-by-line. This is referred to as impulse-type display. LCD displays pictures in a different way. The LCD screen is composed of numerous pixels arrayed in rows and columns. Each pixel stores a graphic data. To display a picture, the LCD screen loads pixel data of a complete frame in parallel. Each pixel keeps its graphic data until being reloaded. At any given time, every pixel of the entire screen is lightened. Hence, LCD can hold still the complete picture to be displayed, so it displays pictures frame-by-frame. This is referred to as holding-type display.
A major drawback of holding-type display is the picture blurring caused by frame switching when displaying moving objects. Because the previous frame will never completely disappear from the screen before the next frame comes in. The most straightforward way to solve this problem is to make the previous frame disappear completely by inserting an extra dark frame before the next frame comes in. This will require some efforts on graphic processor. Another simpler solution is to shut off the backlight module of the LCD device for a specific period of time to create a momentary dark image. This dark image neutralizes human eyes from the previous frame and makes them ready to accept the next one. This is referred to as flashing backlight technology. To further eliminate blurring of holding-type display and mimic impulse-type display, an LCD backlight module is divided into several light zones. Each zone can be turned on and off sequentially. A specific control timing sequence is used to turn on and off each light zone. This timing sequence is synchronized to the frame data reload timing to optimize the motion picture quality. This is referred to as sequential flashing backlight technology. Since this sequential flashing backlight technique turns on and off a number of individual light zones, this can also be applied to power-saving and brightness-dimming control.
In some related arts, analog phase delay array is adopted to do the backlight on/off control. However, the timing sequence is adjusted by altering resistance or capacitance value of the control circuit. Therefore, it is an important subject to provide a digital programmable control for making the timing adjusting easier.